Exam Three

The sodium-potassium exchange pump stabilizes resting potential of the neuron membrane at about __________.

-70 mV

The cross-bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?

A myosin head bound to actin

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?

A series of proteins that control calcium release. When action potentials propagate along T-tubules, a voltage-sensitive protein changes shape and triggers a different protein to open its channels, resulting in the release of calcium from the terminal cisternae.

During neuromuscular transmission, the axon terminals release __________.

ACh

Which of the following situations could contribute to prolonged muscle contraction?

ACh not being produced COULD CONTRIBUTE limited availability of calcium ions infrequent neural stimulus cross-bridge formation being reduced COULD NOT CONTRIBUTE

What is the primary role of the enzyme acetylcholinesterase (AChE) at a cholinergic synapse?

AChE degrades acetylcholine in the synaptic cleft.

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross-bridge detachment?

ATP binds to the myosin head. The binding of ATP to the myosin head weakens the bond between myosin and actin, forcing the myosin head to detach. ATP also provides the energy for the next power stroke.

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?

Acetylcholine is degraded by acetylcholinesterase. Acetylcholinesterase is an enzyme that degrades acetylcholine. This degradation results in a rapid cessation of the acetylcholine signal and a swift removal from the cleft.

The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?

Acetylcholine is released by axon terminals of the motor neuron.

Which of the following best describes the role of calcium in synaptic activity?

Calcium influx into the synaptic terminal causes vesicle fusion with the plasma membrane and the release of neurotransmitter.

Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?

Calcium ions are stored in the sarcoplasmic reticulum. Sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle fibers. The sarcoplasmic reticulum is very elaborate in skeletal muscle fibers, allowing for significant storage of calcium ions.

What specific event triggers the uncovering of the myosin binding site on actin?

Calcium ions bind to troponin and change its shape. The shape change caused by the binding of calcium to troponin shifts tropomyosin away from the myosin binding sites on actin.

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?

Calcium ions. Action potentials propagating down the T-tubule cause a voltage-sensitive protein to change shape. This shape change opens calcium release channels in the sarcoplasmic reticulum, allowing calcium ions to flood the sarcoplasm. This flood of calcium ions is directly responsible for the coupling of excitation to contraction in skeletal muscle fibers.

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?

Calcium release from the sarcoplasmic reticulum initiates the contraction.

Which of these is/are true of cardiac muscle fibers?

Cardiac fibers have a long twitch duration compared to skeletal fibers. Cardiac fibers have a single nucleus. Cardiac fibers branch.

When does cross bridge cycling end?

Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin. The sarcoplasmic reticulum contains Ca2+-ATPases that actively transport Ca2+ into the SR. Without Ca2+, troponin returns to its resting shape, and tropomyosin glides over and covers the myosin binding sites on actin.

The neurotransmitter glutamate opens channels that are permeable to sodium ions. What effect does glutamate produce on a postsynaptic neuron?

EPSPs

Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?

Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?

Leak channels

What prevents the Na+ and K+ gradients from dissipating?

Na+-K+ ATPase

What is the role of neurotransmitter at a chemical synapse?

Neurotransmitter binds to receptors on the postsynaptic cell membrane.

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?

RMP

What happens just after an axon is depolarized to threshold?

Some sodium channels open.

Calcium entry into the axon terminal triggers which of the following events?

Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.

How does the myosin head obtain the energy required for activation?

The energy comes from the hydrolysis of ATP. Myosin is a large, complex protein with a binding site for actin. It also contains an ATPase. The energy released during the hydrolysis of ATP activates the myosin head.

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?

The inside surface of the plasma membrane is much more negatively charged than the outside surface.

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients. The resting membrane potential of all cells is negative (inside compared to outside). Therefore, given the direction of the chemical and electrical gradients, more sodium ions diffuse inward than potassium ions diffuse outward.

The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.

The presence of concentration gradients and leak channels

What structure is the functional unit of contraction in a skeletal muscle fiber?

The sarcomere A sarcomere is a regular arrangement of thin and thick myofilaments that extends from one Z disc to the next. A myofibril consists of a series of sarcomeres.

Which of these statements about skeletal muscles is FALSE?

Their fibers branch. (FALSE) They store nutrient reserves. They support soft tissues. They pull on tendons. (TRUE)

The plasma membrane is much more permeable to K+ than to Na+. Why?

There are many more K+ leak channels than Na+ leak channels in the plasma membrane.

The soleus muscle is very red in color. Which of these statements about soleus muscle fibers is FALSE?

They are large in diameter

Female gymnasts can contort their bodies in many different ways and land on a 4" beam with accuracy. Which fiber type is responsible for this ability?

Type A fibers

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?

Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron. There are many more skeletal muscle fibers than there are motor neurons. The ratio of neurons to fibers varies from approximately one to ten to approximately one to thousands.

What type of channel in the postsynaptic membrane binds neurotransmitter?

a chemically gated channel

Which of the following is an example of a presynaptic cell?

a neuron

Sarcomere is best defined as __________.

a repeating functional unit of striated muscle

Which of the following is important to increasing efficiency in tension production?

a shortened relaxation phase IMPORTANT increasing the latent period reducing the size of the zone of overlap increasing calcium reclamation NOT IMPORTANT

A single muscle stimulus will normally be followed by __________.

a single pulse of calcium ion release

The biochemical reaction that consumes the majority of a muscle's ATP is the __________.

actin myosin cross-bridge cycle

In which cell does a graded potential occur?

adipocytes epithelial cells neurons

Muscles are attached to bones by tendons or __________.

aponeuroses

EPSPs and IPSPs summate at the __________.

axon hillock

The simplest level of information processing takes place at the __________.

axon hillock

Events that occur at a cholinergic synapse are listed here, but they are arranged in an incorrect order. Choose the correct order of these events below. (a) Calcium influx triggers exocytosis of ACh. (b) An action potential depolarizes the synaptic terminal. (c) ACh is removed by AChE. (d) ACh binds to receptors on the postsynaptic membrane.

b-->a-->d-->c

Which ion triggers synaptic vesicles to discharge neurotransmitter into the synaptic cleft?

calcium

Triads in skeletal muscle fibers function in __________.

calcium ion release

Smooth muscle contracts when calcium binds to __________ and activates __________.

calmodulin; myosin light chain kinase

The afferent division of the PNS __________.

carries sensory information

Which of these components is usually absent from a neuron?

centrioles ABSENT cell body axons dendrites PRESENT

The effect of a nerve impulse on a postsynaptic neuron depends on the __________.

characteristics of the receptor on the postsynaptic neuron quantity of neurotransmitter released kind of neurotransmitter released by the presynaptic neuron

A muscle producing its maximum tension for a prolonged period is in __________.

complete tetanus

Fatigued muscles signify __________.

decreased pH

Titin is a(n) __________.

elastic protein

Muscle fibers are directly surrounded by which thin layer of connective tissue?

endomysium

The capillaries that wrap around each muscle fiber are located within the __________.

endomysium

Which of these substances is considered a neuromodulator?

endorphins

What mechanism releases neurotransmitter from presynaptic neurons?

exocytosis

The __________ type of muscle fiber has relatively few mitochondria.

fast

Compared to nerve action potentials, muscle action potentials do NOT have __________.

faster proprgation

If EPSPs summate to a sustained value above threshold, then the initial segment will __________.

generate a strong of action potentials

Cardiac muscles cells have a sarcolemma that is more permeable to calcium, which causes them to __________.

have contractions that last longer than skeletal muscle fibers

What is the function of the structure indicated by the arrow?

houses the genetic material (DNA) of the cell

If a nerve cell receives many IPSPs in different locations at the same time, __________.

it will show spatial summation

Muscle fatigue occurs because of a buildup of __________ and a(n) __________ in pH.

lactic acid; decrease

What is the function of the structure indicated by the arrow?

making of energy (ATP), "power house" of the cell

Most CNS neurons fall into which structural category?

multipolar

Saltatory propagation occurs in _________ axons, in which action potentials _________.

myelinated; from one imternode to another

What area of the thick filament binds to actin once its active binding sites are exposed?

myosin cross-bridge (head)

The intercalated disk is NOT a site of __________.

neuromuscular transmission

Which of these neurotransmitters does NOT bind to a plasma membrane receptor?

nitric oxide NOT GABA nopepinephrine sertonin IS

Which of these neurotransmitters is released at CNS adrenergic synapses?

norepinephrine

What is the function of the structure indicated by the arrows?

part of coupling the action potential (electrical event) to contraction (mechanical event)

Which type of ion channel is always open?

passive

Resting smooth muscle can be stretched without affecting tension development because of its __________.

plasticity

The most abundant intracellular cation is __________ while the most abundant extracellular anion is __________.

potassium; chloride

The neurotransmitter GABA blocks presynaptic voltage-gated calcium channels. Consequently, GABA produces __________.

presynaptic inhibition

Which of these is NOT a neuron structural category?

pseudopolar NOT A CATEGORY bipolar multipolar unipolar CATEGORY

Skeletal muscle does each of these EXCEPT __________.

pump blood (DOES NOT) produce movement maintain posture store nutrients (FUNCTIONS)

Which of these is NOT a function of smooth muscle?

pushing blood into the great vessels of the heart NOT elevating skin hairs churning the stomach contents adjusting airway diameter IS

What can the nervous system do to increase muscle tension?

recruit larger motor units increase the number of active motor units increase stimulation frequency

Neuroglia perform all of these functions EXCEPT __________.

release neurotransmitters NOT A FUNCTION provide supportive framework regulate extracellular fluid composition secrete CSF FUNCTION

The action potential in skeletal muscle fibers is first generated on the __________.

sarcolemma

In response to an action potential along the transverse tubules, the __________ release(s) calcium ions into the sarcoplasm.

sarcoplasmic reticulum (SR)

Which of these types of neuroglia are abundant in peripheral ganglia?

satellite cells

Which type of muscle tissue has the greatest effect on the body's heat production?

skeletal

Compared to type A axons, type C axons are __________.

slower propagating smaller diameter unmyelinated

What is the function of the structure indicated by the arrow?

storage of calcium

The __________ nervous system controls glandular secretion.

sympathetic and parasympathetic

What separates the presynaptic and postsynaptic cells at a chemical synapse?

synaptic cleft

The events shown here at a functioning cholinergic synapse cause __________.

synaptic delay

During prorogation of the action potential, __________.

the axon hillock depolarizes the initial segment local currents depolarize a spot adjacent to the active zone after threshold is reached, sodium channels open rapidly

Which region of the sarcomere gives rise to the structure (band or line) indicated by the arrow? (Z line)

the boundary between adjacent sarcomeres

Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

the opening of ligand-gated cation channels These channels permit sodium ions to diffuse inward and potassium ions to diffuse outward.

Which region of the sarcomere gives rise to the structure (band or line) indicated by the arrow? (M line)

the point of connection for adjacent tails of the thick filaments

Which region of the sarcomere gives rise to the structure (band or line) indicated by the arrow? (H band)`

the region of the resting sarcomere that only contains thick filaments

Which region of the sarcomere gives rise to the structure (band or line) indicated by the arrow? (I band)

the region of the sarcomere that contains only thin filaments

Increased muscle fiber endurance can be affected by __________.

the type of activity performed

What is the name given to the regularly spaced infoldings of the sarcolemma?

transverse or T tubules

The muscle action potential penetrates deep into a fiber along the __________.

transverse tubules

What component of the thin filament binds to calcium once calcium is released from the terminal cisternae of the sarcoplasmic reticulum?

troponin

The generation of an action potential in a neuron requires the presence what type of membrane channels?

voltage-gated channels